Mendel and His Peas
Lecture Learning Objectives:
You will be able to:
LO1 – To describe Mendel’s work and the
hypotheses it generated
LO2– To explain how Mendel’s results lead to the
principles of particulate inheritance and
independent inheritance.
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LO1 – To describe Mendel’s work and the
hypotheses it generated
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Observations Driving Mendel’s Work
Plant and Animal Breeders noticed that offspring
(hybrids) of 2 different individuals often displayed
an intermediate like a mix of parental traits.
Hypothesis: Blending
inheritance predicts….
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Controlling Fertilization of the Flowers
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Prediction of Blending Hypothesis
Predict that F1 generation have slightly
wrinkled seeds
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Mendel’s Monohybrid Cross Results
Parental Generation=
pure breeding lines
Offspring – F1
generation–
phenotype of male
parent
Phenotype of female
parent not present
Does this support the Blending
Hypothesis? Why or Why not?
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Where did the Wrinkled Trait Go ?
Critical Experiment –female phenotype in F1 is not
lost, so “blending “did not occur
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Your Turn
Work the monohybrid cross
problems in the handout.
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Think About It……
Thanks to digital photography and programs like
Photoshop, photography studios can claim to predict
what a couple’s child would look like based upon
merging images of the putative parents.
Explain in genetic terms why this is nonsense.
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Mendel’s Unfortunate Naming
Conventions
What is the nature of the dominant allele?
What is the nature of the recessive allele?
Dominate and recessive represent alternative
phenotypes.
Dominant does not imply presence, Recessive does
not imply absence
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Does Gender Influence Trait Inheritance?
The Reciprocal Cross
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Results of Mendel’s 8 Years of Experiments
What do you notice about
the ratio of dominant to
recessive phenotype in
each cross?
Is the distribution of
offspring dependent on
the trait studied?
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The Dihybrid Cross and Independent
Assortment
Do the parental alleles remain together when
gametes are formed?
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Your Turn: Predict the Gametes for
Dependent Assortment
Female Parent: rryy ( green seeds, wrinkled)
Male parent: RRYY (yellow seeds, smooth
Gametes produced by Female Parent:
ry
Gametes produced by Male Parent:
RY
RrYy
Phenotypes of F2 Generation: ¼ RYRY, ½ Ryry, ¼
ryry
Phenotypes of F1 Generation:
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Mendel’s result of Dihybrid Cross
Which of Mendel’s hypotheses is consistent with these
results?
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Your Turn
Work the dihybrid cross
problems in your handout
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But What If You Know The Phenotype
But Not The Genotype: The Test Cross
A test cross reveals an unknown genotype
Why do we care?
Contribution of
homozygous
parent known.
Allows
determination of
2nd parental
phenotype.
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Lecture Summary
How did Mendel’s work discredit the
hypothesis of Blended Inheritance?
What evidence did Mendel use to support
the claim that traits are particulate?
What evidence supports the principle of
independent segregation?
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